This work was carried out at Shandweel Experiment Station, Sohag, Gvernorate from 1998 to 2000 to investigate the effect of inbreeding on some onion bulb characters in the second generation (S₂) of  " Giza 20 " cultivar.           Percentage of single growing point and single center bulbs were increased by inbreeding in the second generation while, internal and external doubles, mean bulb weight, bolters and culls were decreased.                 Predicted gain was more than realized for the single growing point and single center bulb characters while, realized gain was more than predicted in internal and external doubles, bolters, mean bulb weight and culls in S₂ populations.